Signal switching systems are widely used in front end module (FEM) products, such as in radio transceivers, wireless handsets, cable modems, and the like. It is often desirable to direct, route, or electronically switch signals, especially electromagnetic signals in the MHz and GHz range, e.g., radio frequency (RF), intended for transmission over wired or wireless interfaces. For example, a switch may route a signal to one antenna when placed in a first condition (or state) and may route the signal to a second antenna when placed in a second condition. Such capability may be desirable, for example, when the two antennas exhibit differing or varying performance characteristics, or when the two antennas are designed for different frequency bands in which a common transceiver or amplifier may operate, or when transitioning between a transmit and a receive operation, etc.
When a signal switch is in an on state (connected, conducting) it is meant to pass a signal through with minimal loss. Additionally, when the signal switch is in an off state (disconnected, non-conducting) it is meant to reject the signal, i.e., to not allow the signal to pass through or to significantly attenuate any signal passing through.
Signal switches have performance characteristics taken into account when designing the switch, a module, or a device. For example, a switch component has an insertion loss, typically expressed in decibels (dB), representing a reduction in signal strength due to the switch when on. Another performance characteristic of a switch is isolation, also typically expressed in dB, which is a measure of the switch's ability to reject the signal when the switch is off. In general, signal switches are imperfect and allow some signal through even when off (measured as, e.g., “isolation”) and fail to allow the full signal strength through when on (measured as, e.g., “insertion loss”). It is desirable to have low insertion loss when on and high isolation when off.